I looked into a tree visualization library, Treeviz, and talked to the author, Werner Randelshofer. This was a follow-up to a PGV post:
It does very interesting views, but there is a big limitation -- it only does strict trees. Genealogy charts are directed graphs, not trees, because each family has 2 parents. That means it is fine for ancestry, but for descendancy, you can’t list spouses, just the tree of children. Some of those tree views are amazing, though, so it still may be worth adding.
Werner wrote these new tree views on top of an existing hyperbolic tree library, and that original library might work with graphs. I have to look into that yet.
Of course you can list spouses in a descendant chart. PhpGedView and WorldConnect do it. (Though I'm not fond of PGV's style.)
I meant that programs like treeviz that use a strict top-down tree model do not support spouses. Spouses are next to each other, which is outside of the blood line.
One approach (which may look odd to most users) is adding a spouse/family layer in the top-down tree. Instead of:
parent - child - grandchild
parent - spouse/family - child - spouse/family - grandchild
That makes more sense when a man has children from 2 wives -- his children are under 2 different FAMS's, where the FAMS node mentions the spouse.
That's what PGV and WorldConnect do - and the web experiment I put up.
I don't find anything counter-intuitive about it.